Disposable products have revolutionized modern lifestyle and are of great convenience to society. Such products generally are relatively inexpensive, sanitary and quick and easy to use. Disposal of such products, however, increasingly is a problem as landfills close and incineration contributes to urban smog and pollution. Consequently there is an urgent need for disposable products that can be disposed of without dumping or incineration. An ideal disposal alternative would be the use of municipal sewage treatment and private residential septic systems. Products suited for disposal in sewage systems that can be flushed down a conventional toilet are termed "flushable." An essential feature of flushable products is that they must have sufficient wet strength for their intended use, yet lose structural integrity upon contact with water. Meeting these dual criteria is particularly difficult for products that come in contact with body waste fluids, especially urine, due to their similarity to normal tap water, as illustrated in Table 1.
TABLE I ______________________________________ Parameter Infant Urine Tap Water ______________________________________ pH 5.8-8.5 5.0-10.5 Calcium 4-182 ppm 0-145 ppm Magnesium 6-333 ppm 0-120 ppm Sodium 12-6,200 ppm 1-198 ppm Chloride 190-10,320 ppm 0-540 ppm Sulfate 23-3,514 ppm 0-572 ppm ______________________________________
A distinct difference between urine and normal tap water is temperature. The skin temperature within the area enclosed by a disposable diaper is shown in Table 2 (cited from "Factors influencing infant diaper dermatitis" by W. E. Jordan and T. L. Blaney, published in Neonatal Skin, edited by H. Maibach and E. K. Boisits, Marcel Dekker, Inc., New York, 1982.).
TABLE 2 ______________________________________ Skin Temperature Within the Diapered Area (Disposable Diaper) Skin temperature.sup.a Site (.degree.F.) (.degree.C.) ______________________________________ Diapered area Pubic 95.3 35.2 Intertriginous 97.9 36.6 Buttocks 89.4 31.9 Normally exposed skin Abdomen 95.5 35.3 Outer aspect of 90.6 32.6 thigh ______________________________________ .sup.a Study base = 25 infants
Toilet bowl water temperature initially is determined by the temperature of tap water and subsequently approaches room temperature (20.degree. C. to 25.degree. C.) with time. Tap water temperature is effected by the temperatures of ground water and surface water which make up the tap water, as well as ambient room temperature. After toilet bowel water is discharged into the sewage system, the water temperature drops as it moves underground.
The normal temperature of ground water at shallow depths in the United States ranges from a low of about 3.degree. C. to a high of 25.degree. C. The temperature of shallow ground water in a particular locality is determined mainly by the mean annual air temperature of the region. At greater depths, the internal heat of the earth controls the temperature, which on the average, increases approximately one degree Fahrenheit with each additional 50 to 100 feet of depth below land surface. Normal ground water temperatures at a depth of 30 to 60 feet seldom vary more than a degree or so all year long, and at greater depths, remain practically unchanged. The lowest ground-water temperatures (3.degree. C.) are in northern Minnesota and the highest temperatures (25.degree. C.) are in the extreme southern tip of Florida. In the eastern part of the country, ground water temperatures show a more or less regular increase from north to south. Table 3 shows the percent area of the United States that has shallow ground water at a particular temperature range.
TABLE 3 ______________________________________ Temperature above (.degree.F.) (.degree.C.) %, area ______________________________________ 77 25.0 0.1 72 22.2 3.2 67 19.4 14 62 16.7 27 57 13.9 40 52 11.1 59 47 8.3 79 42 5.6 95 37 2.8 100 ______________________________________
The temperature of surface water (lakes, rivers and reservoirs) varies with geographic location and season. In July/August, the highest surface water temperatures (32.degree. C.) are in the south-western part of Arizona and extreme south-eastern parts of California. Table 4 shows the percent area of United States that has surface water at a particular temperature range in July/August.
TABLE 4 ______________________________________ % of area of United States Temperature having surface water temperature (.degree.F.) (.degree.C.) above the indicated temperature ______________________________________ 90 32 1 85 29 3 80 27 24 75 24 45 70 21 69 65 18 92 60 16 99 50 10 100 ______________________________________
It is obvious from this data that only less than 3% of the country and less than two months of the year have surface water temperature above 29.degree. C.
Numerous attempts have been made to produce flushable fibers, fabrics, films and adhesives that retain their integrity and wet strength in the presence of body waste fluids, yet can be disposed of via flushing in conventional toilets. One approach to producing a flushable product is to limit the size of the product so that it will readily pass through plumbing without causing obstructions or blockages. Such products have high wet strength and do not disintegrate during flushing. Examples of this type of product include wipes such as baby wipes. This approach to flushability suffers the disadvantage, however, of being restricted to small sized articles. Many of the current flushable products are limited to such small articles.
Another approach to producing a flushable product is to manufacture a product that is normally insoluble in water, but which disintegrates in the presence of alkaline or acidic aqueous solutions. The end user is provided with an alkaline or acidic material to add to the water in which the product is to be disposed. This approach permits disposal via normal plumbing systems of products substantially larger than wipes, but suffers from the disadvantage of requiring the user to perform the step of adding the dissolving chemical to the water. A further disadvantage is that the inadvertent or intentional disposal of such a product in a conventional toilet without the addition of the dissolving chemical can cause serious obstruction of blockage of the plumbing system. The latter disadvantage can, however, be overcome by incorporating the dissolving acid or alkali into the article but separate from the dissolvable material while in use. The dissolving chemical is only released upon contact with water during flushing.
Similarly, another approach to producing a flushable product, particularly wipes, consists of forming the product from a pH sensitive gelled polymer and storing the product in the presence of a separate acid pH solution. When the wipe is placed in a large quantity of neutral pH water, it disintegrates as a result of the pH shift. A disadvantage of this pH shift approach to flushability is that some acidic polymers lose wet strength at slightly alkaline pH in the range of 7-8. Because the pH of urine may be as high as 8.5, these flushable materials are not well suited for use in, for example, diapers or incontinence pads.
Another approach to producing a flushable product is to combine water soluble material with water insoluble material to form a mixed material product. Upon contact with water, the water soluble material dissolves, reducing the structural integrity of the article, and causing its disintegration, such that it will easily pass through the plumbing system. A similar approach is to blend together a water insoluble material with a water soluble material such that the water insoluble material retards the contact of water with the water soluble material.
Yet another approach to producing a flushable product is to form the product from material that is susceptible to attack by specific enzyme catalysis that breaks down the structural integrity of the material. In such a product the enzymes may be introduced into the disposal water separately. These systems suffer many of the same disadvantages as those described above for alkaline or acid treatable materials. Still another approach to producing a flushable product is to use polyvinyl alcohol polymers, or copolymers wherein one polymer is polyvinyl alcohol, which gel in the presence of borate ions in aqueous solution, but which break down in the presence of large excesses of water as the borate ion diffuses away from the polymer and the borate ion concentration decreases. A major disadvantage of these flushable products is that they must be pre-moistened, and thus, are limited to articles such as pre-moistened wipes. Additionally, the high concentration of boric acid required, while suitable for products that contact the skin only temporarily, may cause irritation upon prolonged contact with skin if used, for example in a diaper or incontinence pad intended to be worn for extended period of time. Furthermore, these polymers when dry are not suitable for use in products such as diapers and incontinence pads because the salt concentration in urine often will be too low to ensure insolubility of the product while in use. Products made of these materials would dissolve during use in the absence of added salt.
Wipes have been made using colloidal cellulose sulfate esters as binders. The colloidal cellulose sulfate esters form aqueous gels in the presence of potassium ions. The immersion in water of such wipes results in the gel breaking and the wipe dispersing.
Still others have attempted to make flushable products wherein a non-woven web is bound together with salt-sensitive binders. For example, some acrylic copolymers precipitate in the presence of high concentrations of calcium ions. The problem with calcium-dependent water soluble binders, however, is that across the country the concentration of calcium in normal tap water varies tremendously. Consequently, flushable products made with those binders may not, in fact, be flushable in regions with high calcium containing water. Water analyses of metropolitan Los Angeles water supplies demonstrate the wide variations that can occur. See, 1982-1983 Analyses of Metropolitan's Water Supplies. For example, one water source had 83 mg/L of calcium whereas another water source had only 16 mg/L of calcium. Similar variances were found for other ions as well, as illustrated by the specific conductance measurements, which ranged from 252 .mu.mho/cm to 1106 .mu.mho/cm.
Not only does the ionic and pH character of normal tap water vary tremendously in different geographic locales, but the salt concentration of body waste fluids, especially urine, varies greatly at different times during the day and under different conditions. Compositional differences in dietary intake lead to tremendous variations in the urinary output of electrolytes. For example, the urinary concentrations of sodium, potassium, chloride, phosphate and urea are lower in breast-fed infants than formula-fed infants. Furthermore the amount of intake affects urine electrolyte composition as more fluid is taken in the concentration of urinary salts decreases. Salt variations in a normal diurnal period can fluctuate .+-.40% from the 24 hour mean concentrations. As a consequence of these variations, prior art flushable compositions often are not suited for all disposable products, especially diapers and incontinence pads.
In the prior art, precipitating salts generally are supplied to the local external environment around the polymeric material. An example is personal care pre-moistened wipes, where precipitating salts are dissolved in the solution surrounding the wipe. This method of introducing salt to flushable material is impossible, however, when the flushable article is provided dry, such as with flushable diapers. Alternatively, salts or other additives may be coated on the external surface of flushable materials. The latter method prevents the salt or additive from quickly washing in the presence of small amounts of water such as perspiration, but provides only a limited functional time for using the flushable article after contact with bodily fluids or wastes, unless excess salt or additive is provided to counteract these effects. The high concentrations of salt or additives required to ensure structural integrity during use, in turn may cause undue irritation to the wearer of the flushable article. What is needed are flushable products having sufficient wet strength for their intended use, which contain polymers that can be made reversibly insoluble in the presence of body waste fluids, but soluble in normal tap water, and therefore flushable in conventional toilets.